Picking on individual lines or couplets as a way of dating shanties is a complete waste of time for reasons that should appear obvious.
Rather, the whole 'feel' of the shanty should be used as a pointer.
I sing two versions of Santi-anna, one pro him and his exploits, and the other more factual which lauds Taylor.
Whenever I sing the pro Santi version I usually say a few words about how this version was sung by British seamen with an axe to grind against the Yanks who had whooped our asses quite recently and how many found themselves in the Mexican Army as soldiers of fortune, and so were biased against those upstart colonials.
The fact that so many singers of shanties have no idea of what they are singing about, and worse, that they try to rationalise the old words with new meanings and going so far as to actually change the words to suit their own ideas is rather depressing. The more folks go down that route the more the original is lost in the mists of time.